Authorities Postpone Revision of Southern Pine Design Values

Last week's meeting of the American Lumber Standards Committee (ALSC) was supposed to be the beginning of the end game in the revision of official design values for Southern Pine dimensional lumber. The Southern Pine Inspection Bureau (SPIB), the official grading agency for the Southern Pine lumber industry, had completed a full round of testing of lumber pulled from member mills, and had proposed new values for compressive strength, modulus of elasticity, and modulus of rupture of the material. The expectation was that the ALSC would approve the new values, which would then, over time, find their way into building codes in the form of shortened span tables — reflecting the basic fact that tree farming techniques have lowered the strength of the wood in recent decades.

But something happened on the way to the forum. Under the American Softwood Lumber Standard published by the US Department of Commerce — the official framework that governs all lumber grading rules and their implementation — the Forest Products Laboratory (FPL) of the United States Department of Agriculture has to review any changes to grade rules or design values. And in this case, the FPL review raised some questions about SPIB's methods and results. After receiving the FPL's feedback, SPIB decided to withdraw its proposal, confer with the FPL over the technical issues, and come back later with a revised proposal.

Said one industry observer: "In short, the proposal was perhaps hastily prepared and upon scrutiny, it was found to be flawed enough to warrant withdrawal — that step being perhaps more favorable than submitting it and finding it to be non-actionable."

The FPL's reservations, and SPIB's response, are unlikely to change the final outcome. It's clear that the trees have changed, and one way or another, code-approved spans for Southern Pine used as floor or rafter framing are going to end up shorter by a foot or two, depending on the dimension, the span, and the loads involved. But that result is going to take just a little bit longer. For now, the ALSC has kicked the can down the road: The committee plans to revisit the issue in January 2013.